The present invention relates to a display device for information signals which is suitable for highly efficient image display of a standard television signal of, for example, NTSC system, a high definition television signal of, for example, high definition system, a television signal of progressive scanning system or a stereoscopic television signal based on television signals of a plurality of channels.
Available as the conventional television system is the standard television system including the NTSC system (or ED system or ED 2 system), PAL system (or PAL plus system) and SECAM system. In the case of the NTSC system, the number of scanning lines per frame is set to N1=525, the field frequency to fV1=59.94 Hz (equivalent to the frame frequency being fV1/2=29.97 Hz), the horizontal scanning frequency to fH1=15.73 kHz and the aspect ratio to 4:3.
On the other hand, with recent improvements in the television system, high definition of image has been promoted and a high definition television (HDTV) system such as high definition system and ATV system in which the number of scanning lines is nearly twice that of the standard television system to drastically improve the image quality has been contrived and is about to be broadcast. In the case of the high definition system, the number of scanning lines per frame is set to N2=1125, the field frequency to fV2=60 Hz (equivalent to the frame frequency being fV2/2=30 Hz), the horizontal scanning frequency to fH2=33.75 kHz and the aspect ratio to 16:9. In high definition image display for use in personal computers, a television signal of progressive scanning type is used and for example, the number of scanning lines per frame is set to N2=1050, the field frequency to fV2=60 Hz (equivalent to the frame frequency being fV2/2=30 Hz), the horizontal scanning frequency to fH2=31.5 kHz and the aspect ratio to 4:3.
In a recent example as reported in, for example, a literature "Conditions Providing for Field-sequence Stereoscopic Vision" (Isono et al, J. Inst. TV Engrs. of Japan, Vol. 41, No.6, pp.549-555, 1987), a study of stereoscopic television in which a stereoscopic image is time-division displayed by using video information signals of two channels based on the aforementioned standard television system has been proceeded with. In this case, of two video information signals of first and second channels, one video information signal of the first channel is assigned with image information (L) for left eye and the other video information signal of the second channel is assigned with image information (R) for right eye. In case the above NTSC system is applied to this stereoscopic television, the number of scanning lines per frame is set to N1=525, the field frequency to fV1=59.94 Hz (equivalent to the frame frequency being fV1/2=29.97 Hz), the horizontal scanning frequency to fH1=15.73 kHz and the aspect ratio to 4:3.
Therefore, a future television system is expected to take a coexistent form of the existing standard television system with the stereoscopic television system using a plurality of channels and the high definition television system and progressive scanning television system of quite different types, and it is preferable that a future display device for television signals be a single device which can selectively display all of the television signals pursuant to the plurality of systems.
In a recent example to meet the above needs, a device has been practiced which can selectively display the standard television signal and the high definition television signal in a high definition receiver set and an example of this type of display device is disclosed in, for example, JP-A-6-225269.
In the aforementioned conventional display device for television signals which selectively displays the standard television signal and high definition television signal, however, the standard television signal and the high definition television signal which are different from each other in signal format (especially, horizontal scanning frequency) are switched for display and therefore, deflection systems which are greatly different for the two modes must be operated independently, having difficulties with reduction of the cost of the device.
For an increase in cost of the device, the existing standard television signal is displayed with the conventional image quality at the most, facing disadvantages that on a large-sized display (such as a Braun tube) of high brightness and high definition, various kinds of disturbances including a flicker disturbance and a line structure become conspicuous and the image quality is adversely deteriorated to degrade the performance meeting the cost.
The aforementioned JP-A-6-225269 discloses the display device for television signals adapted to selectively display the standard television signal and high definition television signal but neither considers at all stereo display of the stereoscopic television signal nor discloses at all measures for improving the monaural display image quality of the standard television signal.
In the above literature by Isono et al, an example of a stereo display device for stereoscopic television signals is disclosed but neither monaural display of the high definition television signal and standard television signal nor image quality improvements of the monaural display are disclosed at all; and a stereoscopic television conformable to the standard television system is disclosed but any stereoscopic television conformable to other television systems is not disclosed.
Therefore, in the light of the fact that conditions of putting images of various media in service will come up, realization of a device has been desired strongly which can be a single device capable of performing image display of not only the standard television signal but also the stereoscopic television signal, high definition television signal and progressive scanning television signal and at the same time attaining high image quality.